For an image forming apparatus of an electrophotographic type, there have been proposed a direct tandem-type color printer having a plurality of photosensitive members provided in correspondence to respective colors and configured to directly transfer developer images formed on the respective photosensitive members to a sheet.
For example, there have been proposed a color printer having four photosensitive drums provided in correspondence to respective colors of black, yellow, magenta and cyan, a conveyance belt conveying a sheet with contacting all the photosensitive drums and four transfer rollers provided in correspondence to each of the four photosensitive drums.
In the related-art color printer, a transfer current is supplied between the photosensitive drums and transfer rollers for color printing at a monochrome printing operation. Thereby, the related-art color printer suppresses a reverse transfer of a monochrome image from a sheet to which the monochrome image is transferred to the color photosensitive drums.